Transportation & Fuel Source Technology

Diesel- and Hybrid-Powered Vehicles Can Provide More Societal Benefits than Gas-Powered Autos

Cars and light trucks powered by advanced diesel technology or hybrid technology can provide larger societal benefits than traditional gasoline-powered automobiles, according to a RAND Corporation working paper presented today.

The research by RAND, a non-profit research organization, also found that light trucks and cars continuously fueled by a mixture of 85 percent ethanol and 15 percent gasoline - known as E85 - compare unfavorably with the other two alternatives.

"Rising oil prices coupled with concerns about global climate change are driving debate about which fuels and engines should be used to power the 17 million new cars and trucks sold each year," said John Graham, dean of the Pardee RAND Graduate School and senior author of the research paper.

"Advanced diesel and hybrid technologies show very well in this study, in terms of benefits to the individual and society overall," Graham said. "E85 simply doesn't provide the same benefits."

Graham presented the results of the research today at the annual meeting of the Association for Public Policy Analysis and Management in Washington, D.C. The peer-reviewed paper is available online as part of RAND's working paper series in which initial research results are shared publicly to solicit additional technical feedback.

The research examines the benefits and costs of three alternatives to the gasoline-powered internal combustion engine for the 2010-2020 period: gasoline-electric hybrid technology (as found in the Toyota Prius or the Ford Escape SUV Hybrid), advanced diesel technology (such as the Mercedes-Benz E320 sedan), and dual-fuel vehicles that are powered continuously by E85.

Each alternative has the technological potential for significant market penetration in the near term, the research finds.

Additionally, each technology was compared to a gasoline-powered vehicle. Comparisons were made for three vehicle types: a mid-sized car, a mid-sized SUV and a large pick-up truck. The cost-benefit comparisons were made from the perspective of individual consumers and society in general, on a per-vehicle basis over the life of the vehicle.

The paper ranks the four technologies using benefit-cost analysis. Using most reasonable assumptions, the results placed advanced diesel technology first, followed by hybrid technology, the gasoline engine and E85 technology.

The consumer perspective accounted for technology cost, fuel savings, mobility and performance. The societal perspective also included tailpipe pollutants, greenhouse gas emissions and "energy security costs" for the fuels - the costs to society as a whole from greater dependence on expensive and unstable foreign oil supplies.

Fuel taxes are excluded in the societal case, which is typical of benefit-cost analysis. And the costs are estimations that illustrate relative performance.

The results assume fuel prices of $2.50 per gallon for gasoline, $2.59 per gallon for diesel fuel, and $2.04 per gallon for E85 (including tax credit). The report also examines scenarios where fuel costs are much higher and much lower.

Among the key findings from the consumer perspective:

For all three vehicle types, the advanced diesel offers the highest savings over the life of the vehicle among the options considered. These savings increase with the size and fuel use of the vehicle: $460 for the car, $1,249 for the SUV and $2,289 for the large pick-up truck;

The hybrid option has smaller but still considerable savings for SUV applications ($1,066), moderate savings for pick-up applications ($505) but minimal savings over the life of the vehicle for car owners ($198);

The vehicles operating on E85 cost all three owners more over the vehicle life, with a greater net cost burden for larger vehicles and increased fuel consumption: (-$1,034 for cars, -$1,332 for SUVs, -$1,632 for pick-ups).

Both the hybrid and diesel vehicles are more fuel efficient than their gasoline-powered counterparts: 25 to 40 percent better for hybrid and 20 to 30 percent for diesel, depending on the vehicle.

"While it is assumed that the hybrid vehicle will save more fuel than the advanced diesel, the overall advantage goes to the diesel because of its lower technology costs and better performance such as increased torque," Graham said. "For E85, it is the cost of producing the fuel, not vehicular changes, that drives the negative results."

The key findings from the societal perspective are similar to those of the consumer perspective, including:

The advanced diesel again shows the most promise, particularly for the larger vehicles: $289 for cars, $1,094 for SUVs and $2,199 for large trucks.

The net benefits for hybrids are somewhat less positive, with moderate-to-small values of $481 for SUVs and $132 for light trucks, and an increased cost for cars (-$317) over the life of the vehicle

Results for E85 remain uniformly negative, even more so for larger than smaller vehicles: -$1,046 for cars, -$1,500 for SUVs and -$2,049 for light trucks

"While the net benefit of E85 is generally unfavorable compared to hybrid and advanced diesel technology, the diesel's edge over the hybrid is not as significant," Graham said. "If the cost of hybrid technology falls significantly, the benefits of the hybrid could equal or exceed the diesel."

The report finds that E85 does not generate net societal benefits unless a breakthrough reduces ethanol production costs or gas prices stay near their current high levels for a sustained period of time.

"Hybrid and diesel technology are close, but diesels have the advantage for the typical motorist, and provide a strong edge for drivers who require towing, hauling and rugged capabilities such as those offered in pick-ups," Graham said. "Hybrids have a competitive edge for urban consumers who experience more stop-and-go city traffic."

Graham said it is unlikely that market forces alone will result in widespread use of any of the three technologies, noting that federal consumer tax credits improve the benefit-cost estimates of the advanced diesel and hybrid technologies.

The research was funded through philanthropic support for the Pardee RAND Graduate School, including contributions by DaimlerChrysler, The Dow Chemical Company, DuPont, Ford Motor Company, General Electric, General Motors and Toyota.